an idea ennobled by the faith that our nation can summon from its myriad diversity the deepest measure of unity. An idea infused with the conviction that America's long heroic journey must go forever upward.

这是美国总统克林顿1993年1月20日的就职演讲中的两句话，我想把前面的句子放在一起可以更好地理解：

In serving, we recognize a simple but powerful truth, we need each other. And we must care for one another. Today, we do more than celebrate America; we rededicate ourselves to the very idea of America，an idea born in revolution and renewed through two centuries of challenge. An idea tempered by the knowledge that, but for fate we, the fortunate and the unfortunate, might have been each other. An idea ennobled by the faith that our nation can summon from its myriad diversity the deepest measure of unity. An idea infused with the conviction that America's long heroic journey must go forever upward.

在奉献过程中，我们认识到相互需要这一简单而又强大的真 理。我们必须相互关心.今天，我们不仅是在赞颂美国，我们再一次把自己奉献给美国的理想：这个理想在革命中诞生，在两个世纪的挑战中更新；这个理想经受了认识的考验，大家认识到，若不是命运的安排，幸运者或不幸者有可能互换位置；这个理想由于一种信念而变得崇高，即我国能够从纷繁的多样性中实现最深刻的统一性，这个理想洋溢着一种信念：美国漫长而英勇的旅程必将永远继续。

注：贴出自己的答案后，在网上发现更好的译文，就取而代之了。总该将最好的提供给提问者吧。

参考文献：http://news.sina.com.cn/2009/0120/195.html